Spatio-temporal dynamics of fish feeding in the lower Mulgrave River, north-eastern Queensland: the influence of seasonal flooding, instream productivity and invertebrate abundance

Abstract

Wet-season flooding causes dietary shifts in tropical freshwater fish by regulating instream productivity, habitat structure and food availability. These dynamics have been comprehensively documented worldwide, but data are limited for Australia’s Wet Tropics rivers. The aim of the present study was to extend our earlier fish–habitat model for these systems by examining the role of trophic dynamics in determining fish assemblage composition. Chlorophyll a and phaeophytin concentrations, benthic and littoral invertebrates and fish were collected at four sites in the lower Mulgrave River under a range of flow conditions. Wet-season flooding caused significant reductions in instream productivity, whereas habitat disturbance reduced densities and abundances of littoral and benthic invertebrates. However, volumetric gut contents of 1360 fish, from 36 species, revealed seasonal shifts in guild membership by only two species, with fish moving between sites to target their preferred prey items – largely irrespective of differences in habitat structure. As a result, the food consumed by the fish community present at each site closely reflected the seasonal availability of food resources. The present paper questions whether fish community composition in small tropical rivers can be accurately predicted from habitat surrogates alone and encourages consideration of constraints imposed by the trophic dynamics and reproductive ecology of fish.

Climate change and its implications for Australia's freshwater fish

“…However, the effects of increased flow seasonality and duration of dry periods (Table 1) is likely to result in greater upstream tidal penetration, longer water-residence times and increased water temperatures (Rayner et al 2008). Increased water extraction for human use also has the potential to exacerbate these effects, with implications for water quality, habitat availability, riparian vegetation structure, instream productivity and ultimately fish assemblages Rayner et al 2009). For example, climate-induced alterations to the structure of riparian vegetation communities could affect the availability and consumption of riparian fruits by khaki grunter (Hephaestus tulliensis) (Rayner et al 2009).…”

“…For example, climate-induced alterations to the structure of riparian vegetation communities could affect the availability and consumption of riparian fruits by khaki grunter (Hephaestus tulliensis) (Rayner et al 2009). Increases in water-residence time, instream temperature and autochthonous production could advantage alien species such as black mangrove cichlid (Tilapia mariae) that consume filamentous algae -a niche that appears under-utilised by native species (Rayner et al 2009). Increases in the intensity of cyclones and rainfall events will result in a concurrent change in flood-disturbance regimes (Eliot et al 1999;Williams et al 2003), and disrupt the seasonal cycle of fish-assemblage structure and function (T. Rayner, unpubl.…”

“…Increased water extraction for human use also has the potential to exacerbate these effects, with implications for water quality, habitat availability, riparian vegetation structure, instream productivity and ultimately fish assemblages Rayner et al 2009). For example, climate-induced alterations to the structure of riparian vegetation communities could affect the availability and consumption of riparian fruits by khaki grunter (Hephaestus tulliensis) (Rayner et al 2009). Increases in water-residence time, instream temperature and autochthonous production could advantage alien species such as black mangrove cichlid (Tilapia mariae) that consume filamentous algae -a niche that appears under-utilised by native species (Rayner et al 2009).…”

Short-term movement of barramundi in a ­seasonally closed freshwater habitat

“…Resale or republication not permitted without written consent of the publisher Aquat Biol 12: 147-155, 2011 (Rayner et al 2009). Although the broad impacts of seasonal hydrological changes are well studied, how species respond to these changes requires further study (Arrington & Winemiller 2006, Castello 2008.…”

“…Some authors suggest that prey base is increased in the wet season due to some species breeding after rainfall begins (e.g. Douglas et al 2005), whereas others suggest that prey base is reduced because of wet season flooding, causing habitat disturbance and reductions in productivity (Rayner et al 2009). Although the broad impacts of seasonal hydrological changes are well studied, how species respond to these changes requires further study (Arrington & Winemiller 2006, Castello 2008.…”